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Abstract:
A three year long record of regular vertical aircraft profiling for continuous atmospheric CO2 mixing ratio measurements as well as for flask sampling to derive the climatology of other greenhouse gases (CH4, SF6 and N2O), is presented. Measurements were undertaken in the lower troposphere between 100 and 3000 m over the eastern European taiga about 100 km south east of the city of Syktyvkar (61°24′N, 52°18′E). From the continuous profiles mean CO2 mixing ratios were calculated for the atmospheric boundary layer (ABL) and for the “free troposphere” up to 3000 m. The amplitudes of the respective seasonal cycles are 22.1 ± 3.5 and 14.0 ± 2.1 ppm. ABL mixing ratios are generally larger than free tropospheric values during the winter period, and smaller during the summer due to the change of the continental biosphere from a source to a sink. The phasing of the seasonal cycles is slightly different between the two height intervals (by about 30 days), with the ABL extremes occurring earlier. Very abrupt concentration changes up to 8 ppm are observed in the free troposphere associated with changes in air mass origin. Mean CO2 mixing ratios derived from flask samples at 3000 m compare well with the respective integrated values measured in the continuous profiles above the ABL (ΔCO2 = 0.3 ± 1.6 ppm). CH4 mixing ratios also show a pronounced seasonality, and winter time vertical gradients correlate well with those of CO2. Similarly, SF6 vertical gradients are correlated with CO2 gradients possibly pointing to some anthropogenic origin of the boundary layer CO2 signal during winter. N2O and SF6 also show a slight seasonality with almost the same phasing. The main reasons for the seasonality of both gases are probably transport processes with a possible contribution from stratosphere/troposphere exchange.
